(a) Field of the Invention
The present invention relates to a communication system in a bi-directional dual ring network, and a method thereof. More specifically, the present invention relates to a node system, a bi-directional dual ring communication system having a function of controlling communication congestion between node systems, and a communication method thereof.
(b) Description of the Related Art
In a ring network comprised of nodes having a dual ring access function and being capable of bi-directional data transmission, each of the nodes transmits its packet using a desired bandwidth in a normal state without congestion, but if congestion occurs, it controls the congestion using a congestion control algorithm.
More specifically, the individual nodes check the bandwidth for packet forwarding (providing a packet received from a second node to a third one) and the bandwidth for packet transmission (providing an intrinsically generated packet to a second node). If it is impossible to transmit as many packets as desired because the bandwidth for packet forwarding is excessively large, then the corresponding node considers that congestion occurs, and informs the upper node of its transmission amount according to the congestion control algorithm.
If the transmission bandwidth is larger than the received bandwidth, then the node receiving the information about the transmission amount lowers its transmission bandwidth to the received bandwidth, and forwards the received bandwidth to an upper node. Otherwise, if the transmission bandwidth is smaller than the received bandwidth, then the node informs the upper node of its transmission bandwidth. This procedure relieves the congestion. After relief of the congestion, each node gradually increases its transmission amount.
This method, which has the individual nodes independently perform congestion control, controls the congestion more rapidly and allocates the transmission bandwidth to each node more flexibly, relative to the method in which a specific node controls all the nodes on the whole ring.
In the method, however, all the nodes involved in the congestion uniformly adjust their transmission bandwidth to the transmission bandwidth of the node detecting the congestion, thus deteriorating the use efficiency of the link bandwidth, and the total bandwidth of the link is reduced, gradually increased, and with the congestion, reduced again, thereby oscillating the used amount of the bandwidth of the link.